The present invention relates to an oil-cooled engine assembly in which after lubricating movable parts of an engine, a lubricating oil is cooled and then returned to circulation for cooling the movable parts again.
In an engine, rotating parts such as a crank shaft and bearings of a connecting rod and sliding parts (hereinafter referred to as movable parts) operate at a high temperature due to friction. The movable parts, which remain at a high temperature, are cooled by lubrication with a lubricating oil. Cooling of the lubricating oil after lubrication may be performed by connecting a lubrication line, which includes an oil cooler and an oil tank, to the engine for circulating the lubricating oil. However, there is a need for a space to locate the oil cooler and the oil tank. In order to achieve miniaturization of a whole structure of the oil-cooled engine assembly including the lubrication line, there is yet room for structural improvement.
The engine assembly, which is arranged to reduce an occupying space of the oil tank, has been proposed in, for example, Japanese Patent Publication No. SHO-63-67077 entitled xe2x80x9cEngine Mounting Assemblyxe2x80x9d and Japanese Patent Laid-Open Publication No. HEI-3-67011 entitled xe2x80x9cOil Supply Structure For Enginexe2x80x9d.
The engine assembly disclosed in Japanese Patent Publication No. SHO-63-67077 is comprised of a mounting base, made of a steel tube which supports the engine, in which the oil tank is formed to be filled with a lubricating oil which is circulated with a first engine-drive pump driven with the engine. That is, the mounting base also plays the oil tank role.
However, the mounting base of the engine assembly forms a member for supporting the engine, causing a restriction in size by itself. Accordingly, a limitation arises in freely determining a capacity for which the oil tank occupies. The presence of the mounting base made from steel tube seems to have more or less effect for dissipating heat of lubricating oil in the oil tank. But, the presence of restriction in the size of the mounting base encounters the limitation in enhancing an adequate heat dissipating area.
The engine assembly disclosed in Japanese Patent Laid-Open Publication No. HEI-3-67011 has a structure wherein a cylinder block of the engine is formed with an oil tank at an outer periphery of a water jacket to contain the oil tank within the cylinder block. Lubricating oil is cooled with coolant water in the water jacket.
However, a functional restriction is encountered in the engine in terms of a shape and a dimension of the cylinder block in the engine assembly. The presence of the oil tank contained in such a cylinder block undergoes a limitation in enhancing an adequate capacity for the oil tank and an adequate heat dissipating area for the oil cooler.
It is therefore an object of the present invention to provide an engine assembly which enables a capacity for storing a lubricating oil and a heat dissipating area for cooling lubricating oil to be adequately obtained while achieving the miniaturization of the oil-cooled engine assembly per se.
According to an aspect of the present invention, there is provided an oil-cooled engine assembly which comprises: an engine; a lubricating oil pump disposed internally of the engine; and a hollow frame body which surrounds the engine and engine accessories including a carburetor and a muffler, supports the engine, and is internally formed with an oil passage through which lubricating oil flows. The lubricating oil pump is connected to the oil passage to allow the lubricating oil, which has lubricated movable parts of the engine, to be air cooled with the frame body. The cooled lubricating oil is subsequently recirculated to the movable parts of the engine.
Since the frame body, which supports the engine, is arranged to surround the engine and the engine accessories, the frame body has an increased total length. The adoption of the hollow frame body allows the frame body to serve as the oil passage through which lubricating oil flows to be air cooled. The increased total length of the frame body results in an increase in a heat dissipating area. Thus, the frame body provides an increased heat dissipating effect. In such a manner, the frame body, which supports the engine, also plays a role as the oil tank and oil cooler, resulting in no need for separately providing the oil cooler and the oil tank to achieve a miniaturization of the whole structure of the engine assembly. In addition, the engine is ranged to incorporate therein the lubricating oil pump. This precludes the lubricating oil pump from protruding from the engine.
Desirably, the carburetor is located at one side of the engine and the aforementioned muffler is located at the other side of the engine. It is desired that a lubricating oil supply conduit is additionally provided for supplying lubricating oil from the frame body component, in the vicinity of the crank chamber of the engine to the lubricating oil pump. Lubricating oil, which is cooled with the frame body, is supplied from the frame body component, which is close proximity to the crank chamber remaining at a lower temperature than the frame body component closer to the muffler, to the lubricating pump. The presence of the lubricating oil return conduit connected to the frame body at a point remote from the high temperature muffler provides no fear of lubricating oil being exposed to a high temperature.
In a preferred form, the frame body is covered with the plurality of cover plates having heat dissipating properties, one of which has an air intake port to allow the cooling fan, which draws outside air from the air intake port, to be mounted to the crank shaft. The plurality of cover plates to be mounted to the frame body serves as respective heat discharging plates. Thermal heat produced by the frame body is dissipated via the plurality of cover plates. Since the plurality of cover plates surround a periphery of the frame body, an increased heat dissipating area is obtained. This results in an increase in cooling efficiency for cooling lubricating oil. Also, inner surfaces of the plurality of cover plates and the surface of the frame body covered with the plurality of cover plates are cooled with outside air drawn by the cooling fan. Thus, the heat dissipating performance of the frame body is further improved. In addition, the presence of the plurality of cover plates to cover the frame body allows the engine and the engine accessories to be concealed, resulting in a reduction in engine noise.
In the engine assembly of the present invention, the power output shaft is detachably connected to the crank shaft of the engine and is rotatably supported with either one of the frame body and the cover plates. It is possible for the power output shaft to be altered according to a kind of load to be driven with the engine. Consequently, there is no need for the crank shaft to be altered in accordance with the load.